Among the conventionally-known lawn mowers is one disclosed, for example, in Japanese Examined Utility Model Publication H-05-22031 (hereinafter referred to as “Patent Literature 1”), where an output shaft extends downward from a power source and a cylindrical section of a blade holder is fitted over a lower end portion of the output shaft, and where a grass cutting blade is attached or mounted to a lower end portion of the blade holder by means of a bolt. For cutting grass by the lawn mower disclosed in Patent Literature 1, grass cutting operation is performed where the grass cutting blade is rotated by rotations of the power source being transmitted to the grass cutting blade via the output shaft and the blade holder.
However, the lawn mower disclosed in Patent Literature 1 tends to present a problem that, during the grass cutting operation, the grass cutting blade and the output shaft can undesirably deform by the grass cutting blade hitting an obstacle, such as a sprinkler. Thus, another type of lawn mower has been proposed, for example, in Japanese Examined Utility Model Publication SHO-61-29 (hereinafter referred to as “Patent Literature 2”), which the grass cutting blade is attached to a lower end portion of the blade holder by means of a shear pin (i.e., impact absorbing member), in order to avoid the aforementioned problem. When the grass cutting blade hit an obstacle, such as a sprinkler, the lawn mower disclosed in Patent Literature 2 can prevent undesired deformation of the output shaft by fracturing the shear pin and thereby preventing transmission of an impact load to the output shaft.
However, the lawn mower disclosed in Patent Literature 2 requires fracturing of the shear pin in order to prevent transmission of an impact load to the output shaft. The shear pin (i.e., impact absorbing member) thus fractured would come off the grass cutting blade and drop down to the ground surface. Therefore, it would take time and labor to pick up the dropped shear pin; in this respect, the lawn mower disclosed in Patent Literature 2 still has a room for improvement.